I've never seen red diesel and use to work as a dock master... (30 yrs ago in college)
I've hear of it, but never actually seen it.

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Red-dyed fuel in the U.S. is reserved for off-road uses such as marine and farm equipment. It indicates that federal road taxes were not paid, but it is not duty-free. Some yachts will pay state sales tax on their fuel, though yachts leaving the country can sign an affidavit to that effect and avoid state sales taxes. Whether sales taxes have been paid or not, all marine fuel sold in the United States is dyed red.

Red-dyed fuel in Germany is duty-free and also reserved for off-road uses but, as in all European Union countries, is only permitted for commercial vessels. Both megayachts fined are private vessels.